Hi bickland
Try connecting the box via a scart lead or RCA (red, yellow and white out puts) to the TV, if the box works OK through these connections you can try then replacing the HDMI cable, if it is still the same through HDMI try connecting it to a different TV to see if works through the HDMI on another TV.
Also you could try if the above don’t work, unplug the box all together (all leads) and leave disconnected over night.
If none of these work then I think your box may have developed a fault, and will have to repaired or replaced.